arm64: dts: lg: Fix SPI controller node names

[ Upstream commit 09bae3b64cb580c95329bd8d16f08f0a5cb81ec9 ]

SPI controller nodes should be named 'spi' rather than 'ssp'. Fixing the
name enables dtc SPI bus checks.

Cc: Chanho Min <chanho.min@lge.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>